The "Rosenberg Diary" was written by Alfred Rosenberg, a leading member of the Third Reich and of the Nazi Party during World War II. Rosenberg was privy to much of the planning for the Nazi racial state, mass murder of the Jewish people and other ethnic groups, planning and conduct of World War II and the occupation of Soviet territory, the release said.

"Thanks to the skill of our investigators, our partnerships within the law enforcement community, and the resolve of prosecutors from the U.S. Department of Justice, we were able to secure the diary and transfer it to the Holocaust Museum for both scholars to study and the public to see," said ICE Deputy Director Daniel Ragsdale. "ICE remains committed to protecting the world's cultural heritage by investigating looted or stolen property and art like the diaries and returning them to their rightful owners."

"The finding and return of the Rosenberg Diary is one more small but significant step towards a full and complete understanding of the depraved mindset of those responsible for the mass killing of Jewish people and ethnic groups during World War II," said U.S. Attorney Charles M. Oberly III, District of Delaware.

"The Museum encourages people to think about why the Holocaust happened and how it was possible in such an advanced society," said U.S. Holocaust Memorial Museum Director Sara J. Bloomfield. "The Rosenberg diary will add to our understanding of the ideas that animated the extremist ideology of Nazism. We are grateful to our partners at ICE who helped us secure this important piece of history, a significant addition in our urgent efforts to rescue the evidence of the Holocaust."

Alfred Rosenberg

The Myth of the Twentieth Century, a book written by Rosenberg, articulated the philosophical underpinnings of national socialist ideology. Rosenberg served as head of the Nazi party's foreign affairs department and as the Reich Minister for the Occupied Eastern Territories, which included the Baltic States, Ukraine and parts of Belorussia. As Reich Minister, Rosenberg played a significant role in the mass murder of the Jewish people in the Occupied Eastern Territories, as well as the deportation of civilians to forced labor camps to support the German war effort. Rosenberg also established and headed an organization, Einsatzstab Reichsleiter Rosenberg (Reichsleiter Rosenberg Taskforce), the mission of which was to loot cultural property from all over Europe.

Rosenberg was a defendant at the Nuremberg Trials in Germany, from 1945 to 1946. He was found guilty on all four counts of the indictment for conspiracy to commit aggressive warfare, crimes against peace, war crimes and crimes against humanity. Rosenberg was hanged Oct. 16, 1946.

Allied forces advancing through Germany seized documents, books, and other records of strategic or tactical importance. After the surrender of Germany in May 1945, governmental authority for Germany was placed into Allied hands. This authority included ownership of all documents created by the defeated German government or captured by Allied forces. To prepare for war crimes trials after the cessation of hostilities, agencies of the U.S. government examined and selected relevant documents as potential evidence.

Among the documents seized by allied forces was the Rosenberg Diary. On Aug. 10, 1945, the U.S. Army received the private papers from the Berlin Documents Control Center. Among these papers, according to the receipt prepared Aug. 15, 1945, were "handwritten diary notes" from the years 1934 to 1944. These included notes, dated 1941, "dealing in the early part of (Apr 41) with the conspiracy to dominate Russia and preparations for this occupation (conferences with HITLER and others)."

Dr. Robert M.W. Kempner, a German lawyer who fled Germany for the United States before the war, is accused of taking the diary. When the war ended, Kempner served as the deputy chief counsel and was the chief prosecutor in the "Ministries Case" at the Nuremberg Trials. Kempner had access to seized Nazi documents in his official capacity as an employee of the U.S. government, the HIS release said. At the end of the Nuremberg Trials, Kempner returned to the U.S. and lived in Lansdowne, Pa. Kempner died in 1993.

In 1999, the U.S. Holocaust Memorial Museum received a collection from the estate of Robert Kempner. Parts of the collection were missing from when the museum had originally surveyed the material two years earlier. The museum suspected Rosenberg's diary was among the lost items and began searching for it.

In November 2012, the U.S. Attorney's Office for the District of Delaware and HSI special agents received information from an art security specialist, who was working with the museum, regarding the search for the Rosenberg Diary. Subsequently, HSI special agents located and seized the Rosenberg Diary with a warrant.